Phosphor-coated light extraction structures for phosphor-converted light emitting devices

ABSTRACT

A conformal thin-film phosphor layer is disposed over a surface of a hemispherical lens, a Fresnel lens, or a microlens array, thereby forming a phosphor-coated light extraction structure. Also disclosed is a phosphor-converted photonic crystal light emitting device that incorporates a thin-film phosphor layer. A wafer-level packaging process incorporating a thin-film phosphor layer is also disclosed herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/617,680, filed on Nov. 12, 2009, which claims the benefit of U.S.Provisional Application Ser. No. 61/114,215, filed on Nov. 13, 2008, thedisclosure of which are incorporated herein by reference in theirentirety.

FIELD OF THE INVENTION

The invention relates generally to light emitting devices and moreparticularly to a thin-film phosphor deposition process for forming athin-film phosphor layer adjacent to light extraction structures oradjacent to semiconductor light emitting devices.

BACKGROUND

Solid-State Lighting through Light Emitting Diodes (SSL-LEDs) involvesthe use of solid-state, inorganic semiconductor light emitting diodes toproduce white light for illumination. Like inorganic semiconductortransistors, which displaced vacuum tubes for computation, SSL-LED is adisruptive technology that has the potential to displace vacuum or gastubes used in traditional incandescent or fluorescent lighting.Advantages of SSL-LEDs over conventional light sources include: (1)higher efficiency and associated energy savings; (2) better colorrendering; (3) small form factor; (4) ruggedness; (5) longer operationallifetime and low maintenance; (6) environmentally friendly; and (7) lowfabrication costs.

Conventional LEDs typically generate monochromatic light with a narrowemission spectrum, and thus typically lack a broad emission spectrum toprovide white light for illumination. In order to generate white lightfrom an LED, a narrowband emission resulting from radiativerecombination in the LED is transformed into broadband white lightspectrum. Such broadband white light spectrum can be generated by threegeneral approaches. A first approach is a wavelength-conversion approachby using an ultraviolet (“UV”) LED to excite multi-color phosphors thatemit visible light at down-converted wavelengths. A second approach is acolor-mixing approach by combining multiple LEDs, each of whichgenerates light of a different color. A third approach is a hybridbetween the two approaches described above. The current generation ofcommercially available white LEDs is primarily based on this hybridapproach. In particular, primary light emitted from a blue InGaN-basedLED is mixed with a down-converted secondary light emitted from apale-yellow YAG:Ce³⁺-based inorganic phosphor. The combination ofpartially transmitted blue and re-emitted yellow light gives theappearance of cool (green-blue) white light. Thus, phosphor coatingtechnology is involved for white LEDs using either thewavelength-conversion approach or the hybrid approach.

Current approaches for phosphor coating are described next. A firstapproach, as depicted in FIG. 1A, is a slurry method involving the useof phosphor grains or particles 1 blended in a liquid polymer system,such as polypropylene, polycarbonate, epoxy resin, or silicone resin.The mixed phosphor slurry is dispensed on or surrounding an LED chip 2,and then the liquid polymer system is dried or cured. The LED chip 2along with the phosphor slurry can be disposed in a reflector cup 3, asdepicted in FIG. 1A. While the slurry method is a convenient phosphordispensing method, a resulting color uniformity of LEDs manufacturedwith this slurry method is typically unsatisfactory, and colored ringscan be observed from different viewing angles. These deficiencies arethe result of: (1) variations in the thickness of a phosphor-containingmaterial surrounding an LED chip can lead to various lengths of opticalpaths before an emitted light escapes a package; and (2) non-uniformphosphor distribution within the phosphor-containing material (becauseof gravity and buoyancy effects) tends to move larger phosphor particlesdownward during a liquid polymer curing process. Moreover, due tovariations in the quantity of phosphor powders dispensed surrounding theLED chip, a white color coordinate tends to vary from device to device.These color variations, in turn, result in a complicated white LED colorsorting process, the so-called color binning, which attempts to managethe color variations by sorting each device according to its white colorcoordinate.

To measure the uniformity of emitted light, the variation in aCorrelated Color Temperature (“CCT”) can be used. A color temperature ofa light emitting device can be determined by comparing its hue with atheoretical, heated blackbody radiator. A temperature, expressed interms of degrees Kelvin, at which the heated blackbody radiator matchesthe hue of the light emitting device is that device's color temperature.An incandescent light source can be close to being a blackbody radiator,but many other light emitting devices do not emit radiation in the formof a blackbody curve and are, therefore, assigned a CCT. A CCT of alight emitting device is a color temperature of a blackbody radiatorthat most closely matches the device's perceived color. The higher theKelvin rating, the “cooler” or more blue the light. The lower the Kelvinrating, the “warmer” or more yellow the light. By measuring the CCT atdifferent light emission angles and comparing this variation amongdifferent light emitting devices, the uniformity of the light producedcan be quantified. A blue LED chip dispensed with a yellow phosphor bythe slurry method can have a typical CCT that varies from about 5,800 Kto about 7,200 K across a range of 1,400 K for light emission angles at±70° from a center light-emitting axis of the LED. Because of thepresence of colored rings, the CCT is typically higher at or near thecenter axis than in the periphery, where the emitted light tends to bemore yellow.

A second phosphor coating method is an Electrophoretic Deposition(“EPD”) method for the manufacture of phosphor-converted white LEDs, asdepicted in FIG. 1B. In the case of EPD, a phosphor is electricallycharged by adding a proper amount of an electrolyte in a liquid solventto form a liquid suspension, and is biased by an electrical field. Then,surface charged phosphor particles are moved to an electrode ofcounter-polarity and coated on the electrode. EPD of the phosphorparticles creates a phosphor layer 4 of relatively uniform thicknessthat can produce white light of greater uniformity and reduced instancesof colored rings. While achieving greater color uniformity, the EPDmethod is generally lacking in its ability to deposit phosphors directlyover an electrically nonconductive surface. In commercial production, aphosphor layer is typically coated directly over a LED chip 5, accordingto the so-called proximate phosphor configuration. This configurationtends to be inefficient in terms of light scattering, since theproximate phosphor layer can direct about 60% of total white lightemission back towards the LED chip 5, where high loss can occur. Anotherdrawback of the EPD method is that certain phosphors are susceptible todegradation by the solvent, thereby limiting the general applicabilityof the EPD method.

More recently and as depicted in FIG. 2, another approach involvesforming a luminescent ceramic plate 6 by heating phosphor particles athigh pressure until surfaces of the phosphor particles begin to softenand melt. The partially melted particles can stick together to form theceramic plate 6 including a rigid agglomerate of the particles. Theluminescent ceramic plate 6 is disposed in a path of light emitted by anLED chip 7, which is disposed over a set of electrodes 8. Whileproviding benefits in terms of robustness, reduced sensitivity totemperature, and reduced color variations from chip to chip, a resultingpackage efficiency can be unsatisfactory due to the proximate phosphorconfiguration.

A scattering efficiency (also sometimes referred to as a packageefficiency) is typically between 40% to 60% for commercially availablewhite LEDs, with efficiency losses due to light absorption by internalpackage components such as an LED chip, a lead frame, or sub-mount. FIG.3 depicts an example of a phosphor-converted white LED with yellowphosphor 31 powered by a blue LED chip 32, where a primary blue light 34undergoing color mixing with a secondary light 35 of yellow color togenerate a white color. A main source of light loss results fromabsorption of light by the LED chip 32. Because the LED chip 32 istypically formed of high-refractive index materials, photons tend to betrapped within the LED chip 32 due to Total Internal Reflection (“TIR”)once the photons strike and enter the LED chip 32. Another potentialsource of light loss results from imperfections in a mirror reflector 33in the LED package.

Several scenarios depicted in FIG. 3 can direct light to the highlyabsorbent LED chip 32. First, a primary light 36 emitted by the LED chip32 can be reflected back to the chip 32 by the phosphor powders 31 or bythe mirror reflector 33. Second, down-converted secondary light 37emitted by the phosphor powders 31 can scatter backward towards the LEDchip 32. Third, both primary light and secondary light 38 can bereflected back towards the chip 32 due to TIR at an air-LED packageinterface. To improve the probability of light escaping from thepackage, a hemispheric lens 39 can be used to reduce instances of TIR atthe air-package interface. To reduce instances of backward scatteredlight striking the LED chip 32, the phosphor powders 31 desirably shouldnot be placed directly over the chip surface, but rather should beplaced at a certain distance from the LED chip 32. Furthermore, athinner phosphor layer would reduce instances of backward scattering ofsecondary light by the phosphor powders 31.

It is against this background that a need arose to develop the thin-filmphosphor deposition process and related devices and systems describedherein.

SUMMARY

Certain embodiments of the invention relate to producing ahigh-efficiency white light emitting device incorporating a thin-filmphosphor layer. Because a light emitting semiconductor device, such asan LED, is typically formed of a high refractive index material, a lightextraction structure is desirably incorporated to reduce TIR of lightwithin an LED package. The light extraction structure can involve using,for example, a hemispherical lens, a microlens array, or a Fresnel lens.The light extraction structure is typically formed of an opticallytransparent or translucent material, which is typically electricallynonconductive. As contrasted to EPD, a deposition method of a thin-filmphosphor layer disclosed herein can be used to form conformal thin-filmphosphor layers directly over an electrically nonconductive surface aswell as an electrically conductive surface. The conformal thin-filmphosphor layer also can be deposited over a flat surface as well as anon-flat surface, such as a convex or concave surface.

Some embodiments of the invention relate to producing a high-efficiencyphosphor-converted light emitting device by disposing a conformalthin-film phosphor layer over a light extraction lens structure.Specifically, one embodiment involves producing a phosphor-coated lensby directly depositing a thin-film phosphor layer on an electricallynonconductive light extraction lens structure, such as a hemisphericallens formed of epoxy, silicone, poly(methyl methacrylate),polycarbonate, glass, or a quartz material. The lens structure coatedwith the thin-film phosphor layer can be connected to an LED to producea high-efficiency remote phosphor configuration. An air gap can beincluded for this remote phosphor configuration to increase the lightextraction efficiency.

Some embodiments of the invention relate to producing a phosphormicrolens by depositing a thin-film phosphor layer over a microlensarray. The phosphor-coated microlens array can be laminated over a lightemitting device to form a high-efficiency phosphor-converted lightemitting device.

Some embodiments of the invention relate to producing a phosphor-coatedFresnel lens by depositing a thin-film phosphor layer over a Fresnellens. The phosphor-coated Fresnel lens can be laminated over a lightemitting device to form a high-efficiency phosphor-converted lightemitting device.

Some embodiments of the invention relate to disposing a substantiallyplanar thin-film phosphor layer over an optical path of a light emittingdevice. For certain LED applications such as backlighting for LiquidCrystal Displays (“LCDs”), a small etendue light beam emitted from alight emitting device is involved. Along this regard, some embodimentsof the invention relate to producing a substantially planar thin-filmphosphor layer that is disposed over a substantially planar surface of alight emitting device. One specific embodiment involves disposing athin-film phosphor layer directly over a surface of a light emittingdevice. Another embodiment involves disposing a thin-film phosphor layerover a light emitting device with an optically transparent ortranslucent planar spacer layer disposed in between.

According to some embodiments of the invention, a photonic crystal arraystructure is effective as a light extraction mechanism for lightemitting devices producing a small etendue light beam. In particular,certain embodiments involve producing a high-efficiencyphosphor-converted photonic crystal light emitting device by disposing asubstantially planar thin-film phosphor layer over a surface of aphotonic crystal array structure, such as a two-dimensional photoniccrystal array structure.

One specific embodiment of the invention relates to a phosphor-coatedlight extraction structure, which includes: (1) a light extractionstructure including a coating surface; and (2) a thin-film phosphorlayer including at least one phosphor powder layer and at least onepolymer layer serving as a binder for the at least one phosphor powderlayer, wherein the thin-film phosphor layer is conformally disposedadjacent to the coating surface of the light extraction structure.

Another specific embodiment of the invention relates to aphosphor-converted light emitting device, which includes: (1) a lightemitting device; and (2) a thin-film phosphor layer disposed in anoptical path of the light emitting device, wherein a thickness of thethin-film phosphor layer is in the range of 1 nm to 100 μm, and thethin-film phosphor layer includes: (a) a first phosphor powder layerincluding first phosphor particles; and (b) a first polymer layeradjacent to the first phosphor powder layer, the first polymer layerserving as a binder for the first phosphor particles.

Another specific embodiment of the invention relates to a method offorming phosphor-converted light emitting devices. The method includes:(1) providing a packaging substrate including an array of submountreflectors, which can be an array of reflector cups; (2) connectinglight emitting devices to respective submount reflectors of thepackaging substrate; (3) providing a phosphor-coated microlens array;(4) connecting the phosphor-coated microlens array to the packagingsubstrate; and (5) dicing the packaging substrate to form individualphosphor-converted light emitting devices.

Another specific embodiment of the invention relates to a method offorming a phosphor-converted light emitting device. The method includes:(1) forming a thin-film phosphor layer adjacent to a hemispherical lens,the thin-film phosphor layer including a parylene-based polymer as abinder material; and (2) connecting the phosphor-coated hemisphericallens to a light emitting device.

Another specific embodiment of the invention relates to a method offorming a phosphor-converted light emitting device. The method includes:(1) forming a thin-film phosphor layer adjacent to a microlens array,the thin-film phosphor layer including a parylene-based polymer as abinder material; and (2) connecting the phosphor-coated microlens arrayto a light emitting device.

A further specific embodiment of the invention relates to a method offorming a phosphor-converted light emitting device. The method includes:(1) forming a thin-film phosphor layer including a parylene-basedpolymer; and (2) connecting the thin-film phosphor layer to a photoniccrystal light emitting device.

Other aspects and embodiments of the invention are also contemplated.The foregoing summary and the following detailed description are notmeant to restrict the invention to any particular embodiment but aremerely meant to describe some embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of some embodimentsof the invention, reference should be made to the following detaileddescription taken in conjunction with the accompanying drawings.

FIG. 1A depicts a proximate phosphor-in-cup configuration of aconventional white LED formed using a slurry method.

FIG. 1B depicts a proximate phosphor configuration of a conventionalwhite LED formed using EPD.

FIG. 2 depicts a proximate phosphor configuration of a conventionalwhite LED formed by lamination with a luminescent ceramic plate.

FIG. 3 depicts typical sources of light losses, including lightscattering by phosphor particles, TIR at material interfaces, and lightabsorption at a surface of a light emitting device.

FIG. 4A depicts a single-color thin-film phosphor film stack formedusing a conformal thin-film phosphor deposition process, according to anembodiment of the invention.

FIG. 4B depicts a multi-color thin-film phosphor composite film stackformed using a conformal thin-film phosphor deposition process,according to an embodiment of the invention.

FIG. 5A depicts a thin-film conformal phosphor film stack deposited onan inner concave surface of a hollow hemispherical light extractionlens, according to an embodiment of the invention.

FIG. 5B depicts a thin-film conformal phosphor film stack deposited on abottom surface of a solid hemispherical light extraction lens, accordingto an embodiment of the invention.

FIG. 5C depicts a thin-film conformal phosphor film stack deposited onan outer convex surface of a hemispherical light extraction lens,according to an embodiment of the invention.

FIG. 6 depicts a batch coating process with thin-film phosphor layersconformally deposited on inner concave surfaces of multiple, hollowhemispherical lenses, according to an embodiment of the invention.

FIG. 7A depicts a phosphor-converted LED with a thin-film phosphor layeron an inner concave surface of a hemispherical lens structure producedusing a conformal thin-film phosphor deposition process, according to anembodiment of the invention.

FIG. 7B depicts a phosphor-converted LED produced with a thin-filmphosphor layer disposed on a bottom surface of a hemispherical lensstructure, according to an embodiment of the invention.

FIG. 7C depicts a phosphor-converted LED with a thin-film phosphor layerdisposed on an outer convex hemispherical lens structure produced usinga conformal thin-film phosphor deposition process, according to anembodiment of the invention.

FIG. 8A depicts the phosphor-converted LED of FIG. 7A with a diffuserlens surrounding a light emitting device, according to an embodiment ofthe invention.

FIG. 8B depicts the phosphor-converted LED of FIG. 7B with a diffuserlens surrounding a light emitting device, according to an embodiment ofthe invention.

FIG. 8C depicts the phosphor-converted LED of FIG. 7C with a diffuserlens surrounding a light emitting device, according to an embodiment ofthe invention.

FIG. 9A depicts a microlens array coated with a thin-film phosphorlayer, according to an embodiment of the invention.

FIG. 9B depicts a phosphor-coated microlens array laminated over asemiconductor substrate, according to an embodiment of the invention.

FIG. 9C depicts a semiconductor substrate laminated with aphosphor-coated microlens array being diced into separatephosphor-converted devices, according to an embodiment of the invention.

FIG. 10A depicts a thin-film phosphor layer disposed over a surface of alight emitting device, according to an embodiment of the invention.

FIG. 10B depicts a thin-film phosphor layer disposed over a lightemitting device with a planar spacer layer in between, according to anembodiment of the invention.

FIG. 10C depicts a thin-film phosphor layer disposed over an LEDpackage, according to an embodiment of the invention.

FIG. 11 depicts a phosphor-converted photonic crystal light emittingdevice, according to an embodiment of the invention.

FIG. 12A through FIG. 13B depict a wafer-level, batch packaging processfor light emitting devices, according to an embodiment of the invention.

DETAILED DESCRIPTION Definitions

The following definitions apply to some of the aspects described withrespect to some embodiments of the invention. These definitions maylikewise be expanded upon herein.

As used herein, the singular terms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to a layer can include multiple layers unless thecontext clearly dictates otherwise.

As used herein, the term “set” refers to a collection of one or morecomponents. Thus, for example, a set of layers can include a singlelayer or multiple layers. Components of a set also can be referred to asmembers of the set. Components of a set can be the same or different. Insome instances, components of a set can share one or more commoncharacteristics.

As used herein, the term “adjacent” refers to being near or adjoining.Adjacent components can be spaced apart from one another or can be inactual or direct contact with one another. In some instances, adjacentcomponents can be connected to one another or can be formed integrallywith one another.

As used herein, the terms “connect,” “connected,” and “connection” referto an operational coupling or linking. Connected components can bedirectly coupled to one another or can be indirectly coupled to oneanother, such as via another set of components.

As used herein, the terms “substantially” and “substantial” refer to aconsiderable degree or extent. When used in conjunction with an event orcircumstance, the terms can refer to instances in which the event orcircumstance occurs precisely as well as instances in which the event orcircumstance occurs to a close approximation, such as accounting fortypical tolerance levels of the manufacturing operations describedherein.

As used herein, the terms “electrically conductive” and “electricalconductivity” refer to an ability to transport an electric current,while the terms “electrically nonconductive” and “electricalnonconductivity” refer to a lack of ability to transport an electriccurrent. Electrically conductive materials typically correspond to thosematerials that exhibit little or no opposition to flow of an electriccurrent, while electrically nonconductive materials typically correspondto those materials within which an electric current has little or notendency to flow. One measure of electrical conductivity (or electricalnonconductivity) is in terms of Siemens per meter (“S·m⁻¹”). Typically,an electrically conductive material is one having a conductivity greaterthan about 10⁴ S·m⁻¹, such as at least about 10⁵ S·m⁻¹ or at least about10⁶ S·m⁻¹, while an electrically nonconductive material is one having aconductivity less than about 10⁴ S·m⁻¹, such as less than or equal toabout 10³ S·m⁻¹ or less than or equal to about 10² S·m⁻¹. Electricalconductivity (or electrical nonconductivity) of a material can sometimesvary with temperature. Unless otherwise specified, electricalconductivity (or electrical nonconductivity) of a material is defined atroom temperature.

As used herein with respect to photoluminescence, the term “quantumefficiency” refers to a ratio of the number of output photons to thenumber of input photons.

As used herein, the term “size” refers to a characteristic dimension. Inthe case of a particle that is spherical, a size of the particle canrefer to a diameter of the particle. In the case of a particle that isnon-spherical, a size of the particle can refer to an average of variousorthogonal dimensions of the particle. Thus, for example, a size of aparticle that is a spheroidal can refer to an average of a major axisand a minor axis of the particle. When referring to a set of particlesas having a particular size, it is contemplated that the particles canhave a distribution of sizes around that size. Thus, as used herein, asize of a set of particles can refer to a typical size of a distributionof sizes, such as an average size, a median size, or a peak size.

As used herein, the term “alkane” refers to a saturated hydrocarbonmolecule. For certain applications, an alkane can include from 1 to 100carbon atoms. The term “lower alkane” refers to an alkane that includesfrom 1 to 20 carbon atoms, such as, for example, from 1 to 10 carbonatoms, while the term “upper alkane” refers to an alkane that includesmore than 20 carbon atoms, such as, for example, from 21 to 100 carbonatoms. The term “branched alkane” refers to an alkane that includes oneor more branches, while the term “unbranched alkane” refers to an alkanethat is straight-chained. The term “cycloalkane” refers to an alkanethat includes one or more ring structures. The term “heteroalkane”refers to an alkane that has one or more of its carbon atoms replaced byone or more heteroatoms, such as, for example, N, Si, S, O, and P. Theterm “substituted alkane” refers to an alkane that has one or more ofits hydrogen atoms replaced by one or more substituent groups, such as,for example, halo groups, hydroxy groups, alkoxy groups, carboxy groups,thio groups, alkylthio groups, cyano groups, nitro groups, amino groups,alkylamino groups, dialkylamino groups, silyl groups, and siloxy groups,while the term “un-substituted alkane” refers to an alkane that lackssuch substituent groups. Combinations of the above terms can be used torefer to an alkane having a combination of characteristics. For example,the term “branched lower alkane” can be used to refer to an alkane thatincludes from 1 to 20 carbon atoms and one or more branches. Examples ofalkanes include methane, ethane, propane, cyclopropane, butane,2-methylpropane, cyclobutane, and charged, hetero, or substituted formsthereof.

As used herein, the term “alkyl group” refers to a monovalent form of analkane. For example, an alkyl group can be envisioned as an alkane withone of its hydrogen atoms removed to allow bonding to another group of amolecule. The term “lower alkyl group” refers to a monovalent form of alower alkane, while the term “upper alkyl group” refers to a monovalentform of an upper alkane. The term “branched alkyl group” refers to amonovalent form of a branched alkane, while the term “unbranched alkylgroup” refers to a monovalent form of an unbranched alkane. The term“cycloalkyl group” refers to a monovalent form of a cycloalkane, and theterm “heteroalkyl group” refers to a monovalent form of a heteroalkane.The term “substituted alkyl group” refers to a monovalent form of asubstituted alkane, while the term “un-substituted alkyl group” refersto a monovalent form of an unsubstituted alkane. Examples of alkylgroups include methyl, ethyl, n-propyl, isopropyl, cyclopropyl, butyl,isobutyl, t-butyl, cyclobutyl, and charged, hetero, or substituted formsthereof.

As used herein, the term “arene” refers to an aromatic hydrocarbonmolecule. For certain applications, an arene can include from 5 to 100carbon atoms. The term “lower arene” refers to an arene that includesfrom 5 to 20 carbon atoms, such as, for example, from 5 to 14 carbonatoms, while the term “upper arene” refers to an arene that includesmore than 20 carbon atoms, such as, for example, from 21 to 100 carbonatoms. The term “monocyclic arene” refers to an arene that includes asingle aromatic ring structure, while the term “polycyclic arene” refersto an arene that includes more than one aromatic ring structure, suchas, for example, two or more aromatic ring structures that are bondedvia a carbon-carbon single bond or that are fused together. The term“heteroarene” refers to an arene that has one or more of its carbonatoms replaced by one or more heteroatoms, such as, for example, N, Si,S, O, and P. The term “substituted arene” refers to an arene that hasone or more of its hydrogen atoms replaced by one or more substituentgroups, such as, for example, alkyl groups, alkenyl groups, alkynylgroups, iminyl groups, halo groups, hydroxy groups, alkoxy groups,carboxy groups, thio groups, alkylthio groups, cyano groups, nitrogroups, amino groups, alkylamino groups, dialkylamino groups, silylgroups, and siloxy groups, while the term “un-substituted arene” refersto an arene that lacks such substituent groups. Combinations of theabove terms can be used to refer to an arene having a combination ofcharacteristics. For example, the term “monocyclic lower alkene” can beused to refer to an arene that includes from 5 to 20 carbon atoms and asingle aromatic ring structure. Examples of arenes include benzene,biphenyl, naphthalene, pyridine, pyridazine, pyrimidine, pyrazine,quinoline, isoquinoline, and charged, hetero, or substituted formsthereof.

As used herein, the term “aryl group” refers to a monovalent form of anarene. For example, an aryl group can be envisioned as an arene with oneof its hydrogen atoms removed to allow bonding to another group of amolecule. The term “lower aryl group” refers to a monovalent form of alower arene, while the term “upper aryl group” refers to a monovalentform of an upper arene. The term “monocyclic aryl group” refers to amonovalent form of a monocyclic arene, while the term “polycyclic arylgroup” refers to a monovalent form of a polycyclic arene. The term“heteroaryl group” refers to a monovalent form of a heteroarene. Theterm “substituted aryl group” refers to a monovalent form of asubstituted arene, while the term “un-substituted arene group” refers toa monovalent form of an unsubstituted arene. Examples of aryl groupsinclude phenyl, biphenylyl, naphthyl, pyridinyl, pyridazinyl,pyrimidinyl, pyrazinyl, quinolyl, isoquinolyl, and charged, hetero, orsubstituted forms thereof.

As used herein, the term “arylene group” refers to a bivalent form of anarene. For example, an arylene group can be envisioned as an arene withtwo of its hydrogen atoms removed to allow bonding to one or moreadditional groups of a molecule. The term “lower arylene group” refersto a bivalent form of a lower arene, while the term “upper arylenegroup” refers to a bivalent form of an upper arene. The term “monocyclicarylene group” refers to a bivalent form of a monocyclic arene, whilethe term “polycyclic arylene group” refers to a bivalent form of apolycyclic arene. The term “heteroarylene group” refers to a bivalentform of a heteroarene. The term “substituted arylene group” refers to abivalent form of a substituted arene, while the term “un-substitutedarylene group” refers to a bivalent form of an unsubstituted arene.Examples of arylene groups include phenylene, biphenylylene,naphthylene, pyridinylene, pyridazinylene, pyrimidinylene, pyrazinylene,quinolylene, isoquinolylene, and charged, hetero, or substituted formsthereof.

Conformal Thin-Film Phosphor Deposition Process

Certain embodiments of the invention relate to the formation of athin-film phosphor layer of substantially uniform thickness that can beconformally disposed in an optical path of a light emitting device, suchas an LED, thereby producing substantially uniform white light withlittle or no colored rings. This thin-film phosphor layer can beprepared by an improved deposition method involving: (1) forming aphosphor powder layer that is substantially uniformly deposited on asubstrate surface; and (2) forming a polymer binder layer to fill gapsamong loosely packed phosphor particles, thereby forming a substantiallycontinuous, thin-film phosphor layer. Phosphor conversion efficiency ofthe thin-film phosphor layer can be significantly improved because athinner layer of a precisely controlled quantity of phosphor powders canbe disposed in an optical path, thereby reducing light scatteringlosses. Also, color homogeneity of the thin-film phosphor layer can besignificantly improved due to substantially uniform deposition ofphosphor particles. One method of forming an uniform, thin-film phosphorlayer is to introduce electrostatic charges among phosphor particlesduring deposition of the phosphor particles. The electrostatic chargesamong the phosphor particles can self-balance and adjust theirdistribution, thereby promoting a substantially uniform distribution ofthe phosphor particles. Another method of forming an uniform, thin-filmphosphor layer is through a phosphor dispensing mechanism, such as ashowerhead mechanism in a deposition chamber, or through a rotationalsubstrate holding mechanism, such as a turn table that holds asubstrate. In addition to improved efficiency and color homogeneity,temperature stability of the thin-film phosphor layer can besignificantly improved because the polymer binder layer can be thermallystable up to at least about 300° C. or more.

Advantageously, white color consistency can be maintained in a tightcolor coordinate by a coating process with precisely controlledquantities of deposited phosphor particles through a phosphor powderdelivery mechanism. White color rendering can be precisely tuned with alayer-by-layer sequential deposition of multi-color phosphors, such asdeposition of a red phosphor layer, deposition of a green phosphorlayer, and then deposition of a blue phosphor layer. The ratio ofmulti-color phosphors can be precisely controlled in a resultingcomposite multi-color phosphor film stack. Thus, the color coordinateand CCT of a white LED fabricated by the phosphor thin-film process canbe precisely controlled. This, in turn, can significantly simplify (oreven avoid) a binning process.

According to some embodiments of the invention, a consistent white colorcoordinate can be achieved from lightly varied blue LED chips by tuningthe dosage of a multi-color phosphor film stack. This color compensationmethod can compensate for color variations of the blue LED chips usingdifferent compositions or amounts of phosphor contents. In such manner,white LED yield can be significantly increased for color sensitiveapplications, such as display backlighting using white LEDs.

According to one embodiment of the invention, a thin-film phosphorcoating method is a batch phosphor coating process. Multiple lightemitting devices can be deposited with thin-film phosphor in one coatingoperation. According to another embodiment of the invention, multipleLED lenses can be deposited with thin-film phosphor in one coatingoperation. Similar to semiconductor chip manufacturing, a manufacturingcost per light emitting device can be significantly reduced, and amanufacturing throughput can be significantly increased by a batchprocess. The deposition process of forming the thin-film phosphor layeris desirably held in a vacuum chamber. However, it will be appreciatedthat the deposition process also can take place in a deposition chamberfilled with an inert gas, such as nitrogen, or in an atmosphericenvironment.

As contrasted to EPD, deposition of a thin-film phosphor layer can beused to form conformal thin-film phosphor layers directly over anelectrically nonconductive surface. The conformal thin-film phosphoralso can be deposited on a non-flat surface, such as a convex or concavesurface of an LED lens.

In accordance with the improved process, a variety of phosphors can beused. Typically, a phosphor is formed from a luminescent material,namely one that emits light in response to an energy excitation.Luminescence can occur based on relaxation from excited electronicstates of atoms or molecules and, in general, can include, for example,chemiluminescence, electroluminescence, photoluminescence,thermoluminescence, triboluminescence, and combinations thereof. Forexample, in the case of photoluminescence, which can includefluorescence and phosphorescence, an excited electronic state can beproduced based on a light excitation, such as absorption of light.Phosphors useful in accordance with the improved process include avariety of inorganic host materials doped by activator ions such as Ce³⁺and Eu²⁺, including garnets (e.g.,(Y_(1-a)Gd_(a))₃(Al_(1-b)Ga_(b))₅O₁₂:Ce³⁺ with a, b≦0.2 or YAG:Ce³⁺),silicates, orthosilicates, sulfides, and nitrides. Garnets andorthosilicates can be used as yellow-emitting phosphors, and nitridescan be used as red-emitting phosphors. However, it will be appreciatedthat various other types of wavelength-conversion materials can be used,including organic dyes. Desirably, phosphors and other types ofwavelength-conversion materials can exhibit photoluminescence with aquantum efficiency that is greater than about 30 percent, such as atleast about 40 percent, at least about 50 percent, at least about 60percent, at least about 70 percent, or at least about 80 percent, andcan be up to about 90 percent or more.

Typically, a phosphor used in accordance with the improved process isprovided in a powder form, namely as a set of particles. To enhancecolor uniformity, the particles desirably have sizes in the range ofabout 1 nm to about 100 μm, such as from about 10 nm to about 30 μm,from about 100 nm to about 30 μm, from about 500 nm to about 30 μm, orfrom about 1 μm to about 30 μm.

In accordance with the phosphor deposition process, the phosphor powdercan be transported and deposited over the substrate surface by inertiaeffects, Brownian movement, thermophoresis, or electrical fields if thephosphor powder is electrically charged. One approach to form asubstantially uniformly distributed phosphor powder layer on thesubstrate surface is to entrain, carry, mobilize, or transport thephosphor powder from a phosphor canister by a set of carrier gases, suchas clean, dry air or an inert gas such as nitrogen, and then spray thephosphor powder through a showerhead mechanism in a vacuum, inert gas,or atmospheric chamber. For some embodiments, it is desirable that thephosphor powder is ionized with the same positive or negativeelectrostatic charge during the phosphor transport process. When thecharged phosphor powder is sprayed and deposited on the substratesurface, the constituent phosphor particles are substantially uniformlydistributed to form a phosphor powder layer resulting fromself-balancing of electrostatic forces among the phosphor particles.Specifically, electrostatic spraying of the phosphor powder involves:

-   -   1) The phosphor powder is transported by an inert carrier gas        from a phosphor powder canister or other phosphor powder source.        Phosphor powder flow volume can be precisely controlled by a        nozzle device or other flow control mechanism.    -   2) The phosphor powder is ionized with the same electrostatic        charge. The operation of ionizing the phosphor powder is        desirable to substantially uniformly deposit the phosphor powder        on the substrate surface. It will be appreciated, however, that        this powder ionization operation is optional, and can be omitted        for certain embodiments.    -   3) If the substrate surface is formed of an electrically        nonconductive polymer material, the substrate surface is ionized        with an opposite electrostatic charge on the substrate surface.        If the substrate surface is formed of an electrically conductive        material, the substrate surface is grounded, such as by        electrically connecting the substrate surface to a ground        potential. The operation of ionizing or grounding the substrate        surface is desirable to substantially uniformly deposit the        phosphor powder on the substrate surface. It will be        appreciated, however, that this substrate surface ionizing or        grounding operation is optional, and can be omitted for certain        embodiments.    -   4) The carrier gas entrains the charged phosphor powder to the        deposition chamber through a showerhead mechanism, thereby        evenly distributing the phosphor powder. The showerhead        mechanism is desirable to substantially uniformly deposit the        phosphor powder on the substrate surface. Alternatively, or in        conjunction, the substrate surface is rotated in the deposition        chamber using a rotational mechanism so that the phosphor powder        can be substantially uniformly deposited on the substrate        surface. It will be appreciated, however, that these mechanisms        are optional, and can be omitted for certain embodiments.    -   5) The phosphor powder is conformally and substantially        uniformly deposited onto the substrate surface. In one        embodiment, the substrate surface is a surface of an LED chip or        surfaces of multiple LED chips. In another embodiment, the        substrate surface is a surface of an LED lens or surfaces of        multiple LED lenses. In another embodiment, the substrate        surface is a surface of a glass or quartz substrate. In another        embodiment, the substrate surface is a surface of a flexible        transparent film, such as one formed of poly(ethylene        terephthalate).    -   6) The phosphor powder is discharged with ionizing (or        de-ionizing) gas.

The ionizing gas neutralizes residual electrostatic charges on thephosphor power. It will be appreciated that this discharging operationis optional, and can be omitted for certain embodiments.

In accordance with the phosphor deposition process, the phosphor powderis ionized with electrostatic charges by one, or a combination, of thefollowing methods:

-   -   Corona charging where electric power is used to generate the        electrostatic charges    -   Triboelectric charging where the electrostatic charges are        generated by friction between the powder and some conduit        surface    -   Induction charging where the powder is charged by induction from        an electrical field

For an electrically conductive substrate, the substrate surface can begrounded to maintain an electric field potential for the deposition ofthe electrostatically charged phosphor powder. Electrostatic chargesalso can be created on the phosphor powder or an electricallynonconductive substrate surface by Tribo frictional charging. Inparticular, when two different materials are brought into contact, therecan be a transfer of charge from one to the other to offset an imbalanceof charges. The magnitude and direction of the charge transfer candepend on a number of factors, including a chemical and electronicstructure of both materials.

An opposite electrostatic charge can be created on an electricallynonconductive substrate surface with the Tribo frictional chargingmethod. For example, negative charges can be created on thenonconductive substrate surface by one, or a combination, of thefollowing:

-   -   Tribo frictional charging is carried out using a Teflon powder        blown through a nonconductive epoxy or silicone resin surface.        The Teflon powder can carry electrons away from the epoxy or        silicone resin surface to render the surface negatively charged.    -   An epoxy surface is rubbed with a Nylon brush or cloth.

The phosphor deposition process provides a number of advantages,including:

-   -   It can be applied to both a near phosphor configuration and a        remote phosphor configuration for phosphor-converted white LEDs.    -   It can be implemented as a layer-by-layer phosphor deposition        process, and can be readily used to form a multi-color phosphor        thin-film stack.    -   The deposition process can be a dry and clean process, without        any solvents.    -   Controlled quantities of phosphors can be used during        deposition, thereby significantly reducing color variations and        binning issues of white LEDs.    -   It can achieve a substantially uniform coating of phosphors by        introducing electrostatic charges among phosphor particles.    -   It can achieve a high phosphor utilization yield during        deposition.

In accordance with the phosphor deposition process, the depositedphosphor layer is initially a loosely packed powder layer. Next, apolymer thin film is deposited to fill gaps among phosphor particles andto form a substantially continuous thin-film layer. To preserve thesubstantially uniformly distributed phosphor layer structure, it isdesirable to use a Chemical Vapor Deposition (“CVD”) process to formthis polymer layer as a binder material for the phosphor particles. Itwill be appreciated that another suitable deposition process can be usedin place of, or in conjunction with, CVD to form the polymer layer.Examples of other deposition processes include other vapor depositionprocesses, such as thermal evaporation, electron-beam evaporation, orphysical vapor deposition, as well as spray coating, dip coating, webcoating, wet coating, and spin coating.

Examples of suitable polymers include a family of conformal coatingpolymers that can be used to form a binding matrix for a thin-filmphosphor layer, according to an embodiment of the invention. Inparticular, the family of polymers corresponds to a family ofparylene-based polymers. Generally, parylene-based polymers correspondto a variety of polyxylylene-based polymers, such as poly(p-xylylene)and its derivatives, and include, for example, polymers having a generalrepeating unit of the formula —CZZ′—Ar—CZ″Z′″—, wherein Ar is an arylenegroup (e.g., un-substituted, partially substituted, or fully substitutedarylene group, such as phenylene), and wherein Z, Z′, Z″, and Z′″ can bethe same or different. In specific embodiments, Ar is C₆H_(4-x)X_(x),wherein X is a halogen such as Cl or F, x=0, 1, 2, 3, or 4, and Z, Z′,Z″, and Z′″ are independently selected from H, F, alkyl groups, and arylgroups (e.g., C₆H_(5-x)F_(x) with x=0, 1, 2, 3, 4, or 5). In onespecific embodiment, Parylene N includes a repeating unit of the formula—CH₂—C₆H₄—CH₂—, and is used as a binder material to form a thin-filmphosphor layer. In another embodiment, Parylene C including a repeatingunit of the formula —CH₂—C₆H₃Cl—CH₂— is used as a binder material toform a thin-film phosphor layer. Parylene C can be produced from thesame monomer as Parylene N, but modified with the substitution of achlorine atom for one of the aromatic hydrogens. In another embodiment,Parylene D including a repeating unit of the formula —CH₂—C₆H₂Cl₂—CH₂—is used as a binder material to form a thin-film phosphor layer.Parylene D can be produced from the same monomer as Parylene N, butmodified with the substitution of two chlorine atoms for two of thearomatic hydrogens. In another embodiment, a partially fluorinatedparylene-based polymer referred to as Parylene F can be used. Parylene Fincludes a repeating unit of the formula —CF₂—C₆H₄—CF₂—, and can beformed from various precursors, such as BrCF₂—C₆H₄—CF₂Br. It will beappreciated that these parylene-based polymers are provided by way ofexample, and a variety of other conformal coating polymers can be used.Examples of other suitable polymers include polyimides,fluorocarbon-based polymers (e.g., poly(tetrafluoroethylene)),poly(p-phenylene vinylene), poly(pyrrole), poly(thiophene),poly(2,4-hexadiyn-1,6-diol), fluorocarbon/organosilicon copolymers,poly(ethylene glycol), and their derivatives. Thermal evaporation ofacrylics also can be used to form a substantially continuous phosphorfilm.

Various parylene-based polymer films and other types of polymer filmscan be formed via a CVD technique of transport polymerization. Transportpolymerization typically involves generating a vapor phase reactiveintermediate from a precursor molecule at a location remote from asubstrate surface, and then transporting the vapor phase reactiveintermediate to the substrate surface. The substrate surface can be keptbelow a melting temperature of reactive intermediates forpolymerization. For example, Parylene F can be formed from the precursorBrCF₂—C₆H₄—CF₂Br by the removal of the bromine atoms to form thereactive intermediate *CF₂—C₆H₄—CF₂*, wherein * denotes a free radical.This reactive intermediate can be formed at a location remote from adeposition chamber, and can be transported into the deposition chamberand condensed over the substrate surface, where polymerization takesplace.

More generally, parylene-based polymer films can be formed from avariety of precursors, such as those having the formula(CZZ′Y)_(m)Ar—(CZ″Z′″Y′)_(n), wherein Ar is an arylene group (e.g.,un-substituted, partially substituted, or fully substituted arylenegroup, such as phenylene), Z, Z′, Z″, and Z′″ can be the same ordifferent, Y and Y′ can be the same or different and are removable togenerate free radicals, m and n are each equal to zero or a positiveinteger, and a sum of m and n is less than or equal to a total number ofsp²-hybridized carbons on Ar available for substitution. In specificembodiments, Ar is C₆H_(4-x)X_(x), wherein X is a halogen such as Cl orF, x=0, 1, 2, 3, or 4, and Z, Z′, Z″, and Z′″ are independently selectedfrom H, F, alkyl groups, and aryl groups (e.g., C₆H_(5-x)F_(x) with x=0,1, 2, 3, 4, or 5). Other suitable precursors include dimers having theformula {(CZZ′)—Ar—(CZ″Z′″)}₂, wherein Ar is an arylene group (e.g.,un-substituted, partially substituted, or fully substituted arylenegroup, such as phenylene), and Z, Z′, Z″, and Z′″ can be the same ordifferent. In specific embodiments, Ar is C₆H_(4-x)X_(x), wherein X is ahalogen such as Cl or F, x=0, 1, 2, 3, or 4, and Z, Z′, Z″, and Z′″ areindependently selected from H, F, alkyl groups, and aryl groups (e.g.,C₆H_(5-x)F_(x) with x=0, 1, 2, 3, 4, or 5).

One aspect of a parylene-based polymer film, or another type of polymerfilm, prepared by the CVD method is that it is a conformal coating withsuperior crevice penetration capability, thereby substantially fillinggaps and voids within a phosphor powder layer. In some instances,Parylene F can achieve the best result for gap-filling, while Parylene Ncan achieve the second best result for gap-filling among the family ofparylene-based polymers. Another aspect of a parylene-based polymer isthat it has superior optical transparency in the visible light spectrum,rendering it a suitable filler material among a photoluminescentphosphor powder. Another aspect of a parylene-based polymer is that itsrefractive index can be adjusted based on chemical composition. In oneembodiment, a multi-layer of parylene-based polymer films can be formedas a composite thin-film phosphor stack. This multi-layer structure canbe formed by depositing a Parylene N film, with a refractive index ofabout 1.66, as a binder material among a phosphor powder, and thendepositing a Parylene F film, with a refractive index of about 1.4,thereby enhancing light extraction due to index matching of the ParyleneF film to ambient environment (e.g., air). It will be appreciated that,in general, this multi-layer structure can be formed by depositing afirst polymer film, with a first refractive index, as a binder materialamong a first phosphor powder layer to form a first phosphor layeradjacent to the substrate surface, depositing a second polymer film,with a second refractive index, as a binder material among a secondphosphor powder layer to form a second phosphor layer adjacent to thefirst phosphor layer, and so on, where the first refractive index isgreater than or equal to the second refractive index.

Using the CVD method, a parylene-based polymer, or another type ofpolymer, can be formed as a substantially continuous film having athickness in the range of a few tens of angstroms to about 100 μm, suchas from about 1 nm to about 100 μm, from about 10 nm to about 100 μm,from about 100 nm to about 100 μm, from about 1 μm to about 100 μm, fromabout 1 μm to about 75 μm, from about 1 μm to about 30 μm, or from about1 μm to about 10 μm. In some instances, the thickness of the film canexhibit a standard deviation of less than about 20 percent with respectto an average thickness, such as less than about 10 percent or less thanabout 5 percent. A thickness of the initially deposited phosphor powderlayer can be in the range of about 1 nm to about 60 μm, such as fromabout 10 nm to about 60 μm, from about 100 nm to about 40 μm, or fromabout 100 nm to about 20 μm. In some instances, the thickness of thephosphor powder layer can exhibit a standard deviation of less thanabout 20 percent with respect to an average thickness, such as less thanabout 10 percent or less than about 5 percent. A distribution of thephosphor powder within the resulting film can be substantially uniformacross an extent of the film, such that a weight density (e.g., mass orweight of phosphor particles per unit volume) or a number density (e.g.,number of phosphor particles per unit volume) can exhibit a standarddeviation of less than about 20 percent with respect to an averagedensity, such as less than about 10 percent or less than about 5percent.

An embodiment of a thin-film phosphor layer prepared by the CVD methodis depicted in FIG. 4A. In FIG. 4A, a single-color phosphor powder layer41, such as a YAG:Ce³⁺-based yellow phosphor, is initially deposited ona substrate surface 42. The substrate surface 42 can be a surface of alight extraction structure, which can be electrically nonconductive asin the case of a flexible plastic substrate. A parylene-based polymerlayer 43 is deposited, and another parylene-based polymer layer 44 isnext deposited. The parylene-based polymer layer 43 serves as a binderor a matrix that at least partially penetrates or surrounds the phosphorpowder layer 41, such that phosphor particles of the phosphor powderlayer 41 are dispersed within the parylene-based polymer layer 43. Itwill be appreciated that the parylene-based polymer layers 43 and 44 canbe formed from the same material or different materials. In someinstances, a refractive index of the parylene-based polymer layer 43 isgreater than a refractive index of the parylene-based polymer layer 44.The resulting phosphor coated structure 46 can be laminated or otherwisedisposed adjacent to a light emitting semiconductor device to form aphosphor-converted light emitting device.

In accordance with a layer-by-layer deposition of phosphor powders, theCVD method can be used to form a substantially uniformly distributedmulti-color phosphor stack. In an embodiment depicted in FIG. 4B, amulti-color phosphor thin-film stack 45 is formed by sequentialdeposition of a blue phosphor powder, a parylene-based polymer as abinder material for the blue phosphor powder, a green phosphor powder, aparylene-based polymer as a binder material for the green phosphorpowder, a red phosphor power, and a parylene-based polymer as a bindermaterial for the red phosphor powder. The resulting phosphor coatedstructure 47 can be laminated or otherwise disposed adjacent to a lightemitting semiconductor device to form a phosphor-converted white lightemitting device, which can emit three down-converted secondary lights ofrespective colors by the phosphors. Thus, a Color Rendering Index(“CRI”) of the phosphor-converted white light emitting device can bereadily tuned, for example, when used in an indoor general illuminationapplication with a warmer white light and improved color uniformity.Another application of the phosphor-converted white light emittingdevice incorporating the multi-color thin-film phosphor stack 45 is forbacklighting of LCDs, where a larger display color gamut can be achievedwith three peak wavelengths corresponding to red, green, and blue lightcolors emitted by red, green, and blue phosphors, respectively.

Light Extraction Structures

Internal reflection at a boundary between an encapsulant layer and airis a common source of light loss within an LED package. To reduce theloss within the encapsulant layer, an air/encapsulant interface isdesirably convex and separated from a light source by a certain distancethat depends on an effective diameter of the light source. In someinstances, the encapsulant layer is formed with such a surface, and thesurface is disposed at a certain distance from a light emitting device,such as an LED, and a reflector to ensure most, or all, of the lightthat leaves the light emitting device can escape from the encapsulantlayer. Along this regard, a hemispherical lens, a microlens array, or aFresnel lens can be incorporated as a light extraction structure orlens.

Incorporating phosphor powders dispersed within a light extraction lenscan sometimes yield light scattering losses within an LED package. Toincrease light scattering efficiency, certain embodiments of theinvention relate to forming a phosphor layer as a thin-film layerdeposited on a coating surface of a light extraction lens.

A light extraction lens is typically formed of an optically transparentor translucent material, which is typically electrically nonconductive.As contrasted to EPD, a deposition method of a thin-film phosphor layerdisclosed herein can be used to form conformal thin-film phosphor layersdirectly over an electrically nonconductive surface as well as anelectrically conductive surface. The conformal thin-film phosphor layeralso can be deposited over a flat surface as well as a non-flat surface,such as a convex or concave surface.

Phosphor-Coated Lens for Light Emitting Devices

A hemispherically shaped lens can be used as a light extraction lensstructure for phosphor-converted white LEDs. According to oneembodiment, the hemispherical lens is coated with a thin-film phosphorlayer, resulting in a structure referred hereto as a phosphor-coatedlens. For a phosphor-coated lens 53 depicted in FIG. 5A, a thin-filmphosphor layer 52 a is conformally deposited on an inner non-flat ornon-planar surface of a hollow hemispherical lens 51 a. As depicted inFIG. 5A, the inner non-flat surface is an inner concave surface having agenerally curved profile, and this inner concave surface defines acavity that faces a light emitting device during use. The lens 51 a canbe formed of an optically transparent material, such as epoxy, silicone,poly(methyl methacrylate), polycarbonate, glass, or quartz. In anotherembodiment, a thin-film phosphor layer 52 b is conformally deposited ona bottom, substantially flat or planar surface of a solid hemisphericallens 51 b, as depicted for a phosphor-coated lens 54 in FIG. 5B. Thisbottom, flat surface faces a light emitting device during use. Inanother embodiment, a thin-film phosphor layer 52 c is conformallydeposited on an outer non-flat surface of a hemispherical lens 51 c, asdepicted for a phosphor-coated lens 55 in FIG. 5C. As depicted in FIG.5C, the outer non-flat surface is an outer convex surface having agenerally curved profile, and this outer convex surface faces away froma light emitting device during use. In the illustrated embodiment, thehemispherical lens 51 c is a solid hemispherical lens, although it isalso contemplated that the hemispherical lens 51 c can be a hollowhemispherical lens. It will be appreciated that the phosphor layers 52a, 52 b, and 52 c depicted in FIG. 5A through FIG. 5C can besingle-color phosphor layers or multi-color phosphor layers. Also, itwill be appreciated that the particular shapes and configurationsdepicted in FIG. 5A through FIG. 5C are provided by way of example, andvarious other embodiments are contemplated. For example, in otherembodiments, the phosphor-coated lenses 53 and 54 also can include athin-film phosphor layer that is conformally deposited on theirrespective outer convex surfaces, and the phosphor-coated lens 55 alsocan include a thin-film phosphor layer that is conformally deposited onits bottom, flat surface.

Another embodiment of a phosphor-coated LED lens involves embedding orincorporating a substantially uniform phosphor powder layer onto asurface of a LED lens according to the phosphor deposition methoddescribed herein. For example, a phosphor-embedded LED lens can beformed as follows:

-   -   Form an LED lens using injection molding of a liquid silicone        gel    -   Form a substantially uniform phosphor powder layer onto a        coating surface of the lens, which is still in a gel form    -   Let phosphor particles precipitate into the liquid silicone gel        surface for a prescribed period of time    -   Cure the liquid silicone gel to solidify into a phosphor        embedded LED lens

FIG. 6 depicts a batch coating process with thin-film phosphor layers 61conformally deposited on inner concave surfaces of multiple, hollowhemispherical lenses 62, according to an embodiment of the invention.Advantageously, the thin-film phosphor deposition process describedherein can be implemented as a batch process, and thin-film phosphorlayers can be substantially simultaneously deposited on surfaces ofdesirable substrates, such as surfaces of LED lenses, thereby enhancingmanufacturing throughput and lowering costs per coating substrate.

FIG. 7A through FIG. 7C depict various embodiments of phosphor-convertedLEDs that can be produced by connecting a phosphor-coated lens (e.g.,the phosphor-coated lenses 53, 54 and 55 depicted in FIG. 5A throughFIG. 5C) to a suitable lead frame, a substantially flat submountreflector, or a cup reflector 72. Connection can be accomplished usingan appropriate encapsulant or adhesive, such as a silicone adhesive.Since a phosphor layer is placed at some distance from a light emittingdevice 74, as depicted in FIG. 7A through FIG. 7C, secondary lightirradiated from the phosphor layer will primarily strike the submountreflector or the cup reflector 72, thus having a reduced probability ofstriking the highly absorbent light emitting device 74 directly. Also,since the phosphor layer is manufactured as a thin-film layer, aresulting scattering efficiency can be significantly improved, such asat least about 90%, at least about 92%, or at least about 95%, and up toabout 99% or more. Furthermore, the phosphor-converted LEDs depicted inFIG. 7A through FIG. 7C can emit white light of greater uniformity. Inparticular, a CCT variation can be no greater than about 1,000 K over a140° (±70° from a center light-emitting axis) range of light emissionangles, such as no greater than about 800 K, no greater than about 500K, or no greater than about 300 K, and down to about 200 K or less.

For the phosphor-converted LEDs depicted in FIG. 7A through FIG. 7C, itis desirable to form a cavity or an air gap 71, 73, or 75 between thethin-film phosphor layer and the light emitting device 74. Whensecondary light irradiated from the phosphor layer scatters backwardtowards the air gap 71, 73, or 75, the backward scattered secondarylight has a higher probability of light reflection because of TIR at theair gap interface, due to the lower refractive index of the air gap(about 1) relative to the phosphor-coated lenses 53, 54 and 55. As aresult, the air gap 71, 73, or 75 tends to deflect secondary lightoutwards so as to escape from the phosphor-converted LEDs, thus furtherincreasing the package efficiency. It will be appreciated that anothersuitable low index material can be included in place of, or inconjunction with, air.

It will be appreciated that a number of variations can be implemented ina manufacturing process to produce phosphor-converted LEDs with athin-film phosphor layer coated on a light extraction lens. For example,the light extraction lens initially can be connected to an LED or otherlight emitting device, and the thin-film phosphor layer next can bedeposited on an outer surface of the light extraction lens to produce aphosphor-converted LED as depicted in FIG. 7C.

Still referring to FIG. 7A through FIG. 7C, an optical cavity (e.g.,corresponding to the air gap 71, 73, or 75) advantageously is formedwith its boundary defined by a reflector layer of the submount reflectoror the cup reflector 72 and the thin-film phosphor layer disposed overthe cup reflector 72. The size and shape of the optical cavity can bedesigned so that a primary light emitted from the light emitting device74 and a secondary light irradiated from the thin-film phosphor layerare well mixed. Advantageously, the irradiation light pattern of thephosphor-converted LEDs depicted in FIG. 7A through FIG. 7C can becontrolled by the size and shape of the optical cavity.

To further improve the efficiency of phosphor-converted LEDs, a smalleroptically transparent or translucent hemispherical lens, such as a lens81, 83, or 85 depicted in FIG. 8A through FIG. 8C, is disposedsurrounding the light emitting device 74. The smaller hemispherical lens81, 83, or 85 can serve as a diffuser lens to extract more primary lightout of the light emitting device 74, such as from about 5% up to about40% more primary light. Micrometer-scale features, such as a randomly ornon-randomly (patterned) roughened surface, can be formed on convexsurfaces of the smaller lenses 81, 83, and 85 to control an irradiationpattern of the primary light emitted from the light emitting device 74.It will be appreciated that the smaller lenses 81, 83, and 85 also canbe implemented as substantially planar microlens arrays disposed overthe light emitting device 74.

Phosphor-Coated Microlens for Light Emitting Devices

A microlens array also can be used as a light extraction structureplaced over a light emitting device. According to one embodiment, themicrolens array is coated with a thin-film phosphor layer, resulting ina structure referred hereto as a phosphor-coated microlens. In FIG. 9A,a thin-film phosphor layer 92 is conformally deposited on a surface of amicrolens array 91 using a conformal thin-film phosphor depositionmethod. In FIG. 9B, the resulting phosphor-coated microlens array 94 islaminated over an LED semiconductor wafer 93. In FIG. 9C, the LEDsemiconductor wafer 93 laminated with the phosphor-coated microlensarray 94 is then diced or singulated into separate phosphor-convertedLEDs 95 a, 95 b, and 95 c.

It will be appreciated that a number of variations can be implemented ina manufacturing process to produce phosphor-converted LEDs with athin-film phosphor layer coated on a light extraction microlens array.For example, the microlens array initially can be manufactured on orlaminated to an LED, and the thin-film phosphor layer next can bedeposited on a surface of the microlens array to produce aphosphor-converted LED. Also, it will be appreciated that a thin-filmphosphor layer similarly can be coated over a Fresnel lens to produce aphosphor-coated Fresnel lens, which can be connected to an LED to form aphosphor-converted LED.

Phosphor-Converted Light Emitting Devices

Some embodiments of the invention relate to disposing a substantiallyplanar thin-film phosphor layer over an optical path of a light emittingdevice, such as an LED. Even though a light extraction lens can bedesirable to increase the light extraction efficiency for a packagedLED, it can sometimes increase the spread of light emitted from thepackaged LED. In some applications incorporating LEDs as a light source,such as LED backlighting for LCDs, a small etendue light beam emittedfrom an LED is involved. Along this regard, some embodiments of theinvention relate to producing a substantially planar thin-film phosphorlayer disposed over a substantially planar surface of an LED structure.

One specific embodiment involves disposing a thin-film phosphor layerdirectly over a surface of a light emitting device. In FIG. 10A, athin-film phosphor layer 102 a formed as described herein is disposedover a light emitting side of a surface of a light emitting device 101a.

Another embodiment involves disposing a thin-film phosphor layer over alight emitting device with an optically transparent or translucentplanar spacer layer in between. As depicted in FIG. 10B, a thin-filmphosphor layer 102 b formed as described herein is disposed over anoptically transparent or translucent spacer layer 103, which, in turn,is disposed over a light emitting side of a surface of a light emittingdevice 101 b.

In another embodiment as depicted in FIG. 10C, a thin-film phosphorlayer 102 c formed as described herein is disposed over a substantiallyplanar surface of a packaged LED, where a light emitting device 101 c isdisposed in a suitable lead frame or cup reflector and is covered withan optically transparent or translucent encapsulant 104, such as epoxyor a silicone resin. It is also contemplated that an air-filled gap orcavity can be included in place of, or in conjunction with, theencapsulant 104 to mix a primary light emitted from the light emittingdevice 101 c and a secondary light irradiated from the thin-filmphosphor layer 102 c. Due to the lower refractive index of the air gap(about 1), backward scattered secondary light has a higher probabilityof being reflecting outward from the packaged LED, thus furtherincreasing the package efficiency. It will be appreciated that anothersuitable low index material can be included in place of, or inconjunction with, air.

Phosphor-Converted Photonic Crystal Light Emitting Devices

Because a light emitting device is typically formed of a high refractiveindex material, a light extraction structure is desirably incorporatedto reduce TIR of light within the light emitting device. One way toimprove LED efficiency is to assist in the extraction of light from thehigh-index light emitting device. For typical InGaN LEDs, a largefraction of energy can be emitted into waveguided modes internal to theLEDs, rather than radiation modes. Light generated inside the LEDs canundergo TIR, and there can be a high probability of light absorptionbefore light can escape from the LEDs. A photonic crystal arraystructure can be effective as a light extraction mechanism for LEDs toproduce a small etendue and highly collimated light beam. Also, aphotonic crystal array structure of periodic variations of refractiveindex can improve light extraction by diffracting waveguided modes outof a light emitting device. Due to a planar two-dimensional periodicphotonic lattice structure, photons can escape along a directionsubstantially perpendicular with respect to the light emitting device togenerate small etendue light. Hence, a convex or hemispherical lensstructure can be omitted for a photonic crystal light emitting device.

In FIG. 11, a cross-sectional view of an embodiment of aphosphor-converted photonic crystal light emitting device is depicted,including a substrate 111, a p-type semiconductor layer 112, an activelayer 113, an n-type semiconductor layer 114, an optically transparentor translucent electrode layer 115, and a thin-film phosphor layer 116.It will be appreciated that the thin-film phosphor layer 116 can beimplemented as a single-color phosphor layer or a multi-color phosphorfilm stack. A photonic crystal structure is formed in or otherwiseadjacent to the semiconductor layer 114, where a set of air holes, gaps,or cavities 117 are etched away from the semiconductor layer 114. Theair holes 117 can be filled with a low refractive index dielectricmaterial. For example, a conformal coating material can be utilized tofill the air holes 117, such as using the so-called gap filling processand with parylene-based dielectric materials, which can be prepared byvapor phase deposition and generally exhibit excellent conformal coatingproperties. It can be advantageous in the phosphor-converted photoniccrystal light emitting device manufacturing process that thesubsequently deposited layers 115 and 116 are formed over a solidsurface, such as with the semiconductor layer 114 filled with a set ofparylene-based polymers. Along this regard, another embodiment of thephosphor-converted photonic crystal light emitting device is to use alow refractive index dielectric, such as Parylene-F or Parylene-N, inplace of the air hole structure 117.

One potential issue with the photonic crystal light emitting devicedepicted in FIG. 11 is that the hole structure in the semiconductorlayer 114 can create current crowding. To facilitate current spreadingin the semiconductor layer 114, the transparent electrode 115, such asan Indium Tin Oxide (“ITO”) electrode, is formed over the photoniccrystal structure. The substantially planar thin-film phosphor layer 116is then disposed over the transparent electrode 115 to form aphosphor-converted photonic crystal light emitting device. It will beappreciated that the thin-film phosphor layer 116 can be disposed eitherby lamination of a prefabricated thin-film phosphor layer or by in-situdeposition of the thin-film phosphor layer 116 over the photonic crystalstructure.

Wafer-Level Packaging Process for Light Emitting Devices

Another embodiment of the invention relates to a wafer-level, batchpackaging process for light emitting devices incorporating a thin-filmphosphor layer described herein. In contrast with conventional packagingprocesses, the wafer-level, batch process can yield packaged lightemitting devices that are thinner and with less lens materials consumed,more consistent performance, and improved reliability. Even moreadvantageously, thinner and more uniform phosphor layers can be disposedas part of the wafer-level process, and the packaged light emittingdevices can have improved efficiencies and greater reliability and canoperate with less heat generated.

As depicted in FIG. 12A, a typical 200-mm aluminum, copper, or siliconwafer substrate 120 can hold as much as 10,000 LED packaging submountreflectors or reflector cups per substrate. Thus, a total cost of thewafer-level packaging process can be shared by the multiple devicesmanufactured per batch. As such, the packaging cost is less per devicein terms of total packaging costs.

One embodiment of the wafer-level packaging process for light emittingdevices includes the following operations:

(1) The packaging substrate 120 is formed with an array of cups ordepressions and using an aluminum, copper, or silicon wafer substrate,as depicted in FIG. 12A. A reflector layer is deposited on the packagingsubstrate 120 to yield an array of reflector cups. It is desirable tohave good reflectivity on a cup bottom or a cup wall so that backwardscattered light can be reflected outward.

(2) Light emitting devices are connected to respective reflector cups ofthe packaging substrate 120. Electrodes of the light emitting devicescan be, for example, wire bonded to the packaging substrate 120.

(3) Phosphor-coated microlens arrays 122 are formed, as depicted in FIG.12B.

(4) The phosphor-coated microlens arrays 122 are connected to respectivereflector cups of the packaging substrate 120, as depicted in FIG. 13A.It is also contemplated that a single phosphor-coated microlens array,which is sized to accommodate multiple reflector cups, can be connectedto the packaging substrate 120.

(5) The packaging substrate 120 with the connected phosphor-coatedmicrolens arrays 122 is diced or singulated to yield individual packagedlight emitting devices, such as a packaged LED 130 depicted in FIG. 13B.

It will be appreciated that the wafer-level packaging process depictedin FIG. 12A through FIG. 13B is provided by way of example, and avariety of other embodiments are contemplated.

While the invention has been described with reference to the specificembodiments thereof, it should be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the true spirit and scope of the invention asdefined by the appended claims. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,method, or process to the objective, spirit and scope of the invention.All such modifications are intended to be within the scope of the claimsappended hereto. In particular, while the methods disclosed herein havebeen described with reference to particular operations performed in aparticular order, it will be understood that these operations may becombined, sub-divided, or re-ordered to form an equivalent methodwithout departing from the teachings of the invention. Accordingly,unless specifically indicated herein, the order and grouping of theoperations are not limitations of the invention.

What is claimed is:
 1. A method of forming a phosphor-converted lightemitting device, comprising: providing a packaging substrate includingan array of submount reflectors; connecting an array of light emittingdevices to the packaging substrate; providing a phosphor-coatedmicrolens array; connecting the phosphor-coated microlens array to thepackaging substrate; and dicing the packaging substrate to formindividual phosphor-converted light emitting devices.
 2. The method ofclaim 1, wherein providing the packaging substrate includes: providingthe packaging substrate including an array of submounts; and depositinga reflector layer on the packaging substrate to form the array ofsubmount reflectors.
 3. The method of claim 1, wherein providing thephosphor-coated microlens array includes: forming a first phosphorpowder layer on a microlens array, the first phosphor powder layerincluding first phosphor particles that are distributed on a surface ofthe microlens array; and forming a first polymer film serving as abinder for the first phosphor particles.
 4. The method of claim 3,wherein the first polymer film includes an organosilicon polymer.
 5. Themethod of claim 4, wherein the first phosphor powder layer and the firstpolymer film are placed in a vacuum chamber.
 6. The method of claim 4,wherein forming the first polymer film includes curing the organosiliconpolymer.
 7. The method of claim 3, wherein providing the phosphor-coatedmicrolens array further includes: forming a second polymer film on thefirst polymer film.
 8. The method of claim 7, wherein the first polymerfilm includes a polymer including a repeating unit of the formula:—CZZ′—Ar—CZ″Z′″—, wherein Ar is selected from (1) an un-substitutedphenylene group, (2) a chlorine-substituted phenylene group of theformula: C₆H_(4-x)Cl_(x), with x being an integer in the range of 1 to4, and (3) a fluorine-substituted phenylene group of the formula:C₆H_(4-x′)F_(X′), with x′ being an integer in the range of 1 to 4, andZ, Z′, Z″, and Z′″ are independently selected from H, F, alkyl groups,and aryl groups.
 9. The method of claim 8, wherein the second polymerfilm includes an organosilicon polymer.
 10. The method of claim 9,wherein the first phosphor powder layer, the first polymer film, and thesecond polymer film are placed in a vacuum chamber.
 11. The method ofclaim 9, wherein forming the second polymer film includes curing theorganosilicon polymer.
 12. The method of claim 3, wherein providing thephosphor-coated microlens array further includes: forming a secondphosphor powder layer on the first polymer film, the second phosphorpowder layer including second phosphor particles that are distributed ona surface of the first polymer film; and forming a second polymer filmserving as a binder for the second phosphor particles, wherein the firstphosphor particles and the second phosphor particles are configured toemit light of different colors.
 13. The method of claim 12, whereinproviding the phosphor-coated microlens array further includes: forminga third phosphor powder layer on the second polymer film, the thirdphosphor powder layer including third phosphor particles that aredistributed on a surface of the second polymer film; and forming a thirdpolymer film serving as a binder for the third phosphor particles,wherein the first phosphor particles, the second phosphor particles, andthe third phosphor particles are configured to emit light of differentcolors.
 14. The method of claim 1, wherein providing the phosphor-coatedmicrolens array includes: forming a phosphor powder layer on a microlensarray, the phosphor powder layer including first phosphor particles andsecond phosphor particles, and the first phosphor particles and thesecond phosphor particles are configured to emit light of differentcolors; and forming a polymer film serving as a binder for the firstphosphor particles and the second phosphor particles.
 15. The method ofclaim 1, wherein providing the phosphor-coated microlens array includes:forming a first phosphor powder layer on a microlens array, the firstphosphor powder layer including first phosphor particles; forming asecond phosphor powder layer on the first phosphor powder layer, thesecond phosphor powder layer including second phosphor particles; andforming a polymer film serving as a binder for the first phosphorparticles and the second phosphor particles, wherein the first phosphorparticles and the second phosphor particles are configured to emit lightof different colors.
 16. A method of forming a phosphor-converted lightemitting device, comprising: providing a light extraction structure; andforming a thin-film phosphor layer on the light extraction structure toform a phosphor-coated light extraction structure, wherein forming thethin-film phosphor layer includes: forming a first phosphor powder layeron the light extraction structure, the first phosphor powder layerincluding first phosphor particles that are distributed on a surface ofthe light extraction structure; and forming a first polymer film servingas a binder for the first phosphor particles.
 17. The method of claim16, wherein the light extraction structure is one of a hemisphericallens, a Fresnel lens, and a microlens array.
 18. The method of claim 16,wherein forming the first phosphor powder layer includes: depositing thefirst phosphor particles on the light extraction structure so as tosubstantially uniformly distribute the first phosphor particles on thesurface of the light extraction structure.
 19. The method of claim 18,wherein forming the first phosphor powder layer further includes:inducing electrostatic charges in the first phosphor particles to adjusta distribution of the first phosphor particles along the surface of thelight extraction structure.
 20. The method of claim 18, wherein formingthe first phosphor powder layer includes: depositing the first phosphorparticles on the light extraction structure, while discharging the firstphosphor particles using an ionizing gas.
 21. The method of claim 16,wherein the first polymer film includes a polymer including a repeatingunit of the formula: —CZZ′—Ar—CZ″Z′″—, wherein Ar is an un-substitutedphenylene group, Z, Z′, Z″, and Z′″ are selected from H, F, alkylgroups, and aryl groups, and at least one of Z, Z′, Z″, and Z′ is nothydrogen.
 22. The method of claim 16, wherein the first polymer filmincludes a polymer including a repeating unit of the formula:—CZZ′—Ar—CZ″Z′″—, wherein Ar is a chlorine-substituted phenylene groupof the formula: C₆H_(4-x)Cl_(x), with x being an integer in the range of1 to 4, and Z, Z′, Z″, and Z′″ are independently selected from H, F,alkyl groups, and aryl groups.
 23. The method of claim 16, wherein thefirst polymer film includes a polymer including a repeating unit of theformula: —CZZ′—Ar—CZ″Z′″—, wherein Ar is a fluorine-substitutedphenylene group of the formula: C₆H_(4-x′)F_(x′), with x′ being aninteger in the range of 1 to 4, and Z, Z′, Z″, and Z′″ are independentlyselected from H, F, alkyl groups, and aryl groups.
 24. The method ofclaim 16, wherein forming the thin-film phosphor layer further includes:forming a second polymer film on the first polymer film, wherein thefirst polymer film includes a first polymer, and the second polymer filmincludes a second polymer different from the first polymer.
 25. Themethod of claim 24, wherein the second polymer is an organosiliconpolymer.
 26. The method of claim 16, wherein the first polymer filmincludes an organosilicon polymer.
 27. The method of claim 16, whereinforming the thin-film phosphor layer further includes: forming a secondphosphor powder layer on the first polymer film, the second phosphorpowder layer including second phosphor particles that are distributed ona surface of the first polymer film; forming a second polymer filmserving as a binder for the second phosphor particles, wherein the firstphosphor particles and the second phosphor particles are configured toemit light of different colors.
 28. The method of claim 16, furthercomprising: connecting the phosphor-coated light extraction structure toa light emitting device.
 29. A method of forming a phosphor-convertedlight emitting device, comprising: forming a light extraction structureusing a polymer gel; depositing phosphor particles on a surface of thelight extraction structure while the light extraction structure is in agel form, wherein the phosphor particles are embedded into the surfaceof the light extraction structure; and curing the polymer gel to form aphosphor-embedded light extraction structure.
 30. The method of claim29, wherein the polymer gel includes an organosilicon gel.
 31. Themethod of claim 29, further comprising: connecting the phosphor-embeddedlight extraction structure to a light emitting device.
 32. A method offorming a phosphor-converted light emitting device, comprising:providing a photonic crystal light emitting device; and forming athin-film phosphor layer on the photonic crystal light emitting deviceto form a phosphor-converted, photonic crystal light emitting device,wherein forming the thin-film phosphor layer includes: forming aphosphor powder layer on the photonic crystal light emitting device, thephosphor powder layer including phosphor particles that are distributedon a surface of the photonic crystal light emitting device; and forminga polymer film serving as a binder for the phosphor particles.